It is old in the art to treat fresh lettuce for preserving the same by dipping the same in a cool (freezing point to 40.degree. F.) aqueous solution of potassium nitrate or sodium benzoate as disclosed in U.S. Pat. No. 2,698,804.
Vegetables and fruits are preserved for fresh product sale in U.S. Pat. No. 2,894,843 by contacting the vegetables such as potatoes with an aqueous solution of a vegetable reducing agent such as calcium sulfate.
In general, although vegetables are treated with certain aqueous solutions as in the above U.S. patents, green beans are not mentioned as one of the treated vegetables in such prior art. Green beans are different in nature from potatoes, apples, etc. in that green beans do not have a relatively impervious skin, but rather have an outer covering with many outwardly projecting hairs that serve as guard hairs to trap fungal and bacterial spores. The resultant trapping of such spores, for example, complicates attempts to preserve the beans.
Green beans have been handled and maintained in a dry state to assist in preserving the beans for fresh green bean product sale. When used, post harvest treatments of fresh green beans involved attempts to air-cool the dry beans in a high humidity and in a non-aqueous environment as set forth in:
1. Wilhelm, L. R., "Forced Ventilation Cooling of Commercial Snap Beans Shipments", ASAE paper. Department of Agriculture Engineering, University of Tennessee, Knoxville, TN., No. 79-6518, p. 9.
2. Sistruck, W., "Influence of Post Harvest Storage of Snap Beans on Chemical and Physical Changes during Canning.", Food Research, Vol. 30, 1965, p. 240.
3. Platenius, et al., "Studies on cold Storage of Vegetables", U.S.D.A. Bulletin 602, p. 3.
Even with the cool air, high humidity treatment, the green beans suffer substantial weight losses beginning immediately after harvesting.
While cool temperatures appeared to slow the respiration and deterioration processes, an article by Gorini and Bouvilli, "Studies on Pre-Cooling and Storage of Some Varieties of Snap Beans", ACTA HORTICULTURE, Vol. 38, June 1974, pp. 507-29, warn green bean processors that it is impossible to cool the beans below 5.degree. C. (40.degree. F.) as such colder temperatures caused unwanted chilling injury to the beans.